Thermionic indicating means responsive to light variations



G W L w 0 D L I-m 5 2 9 13 7 1 v 9 N THERHIONIC INDICATIHG MEANSRESFONSH/B TO LIGHT VARIATIONS Filed July so. 1924 ill ,?atented Nov.17, 1925.

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THERMIONIO innroirrrno Means nnsronsrvn 'ro LIGHT vanm'rrons.

Application filed July- 3Q, 1924. Serial No. 729,165.

To all whom, it may concern:

Be it known that I, Join: Jossrn Dow- LING, a citizen of the Irish FreeState, residing at Rathgar, Dublin, in the county of Dublin, Irish FreeState, have invented Improvements in or Relating to ThermionicIndicating Means Responsive to Light Variations, of which the followingis a specifi cation.

This invention relates to thermionic indicating means responsive tolight variation and it has for its object to effect certainimprovements, the most prominent of which is directed to the productionof an arrangc-' ment that shall be of extreme reliability in use andhence particularly adapted for signalling systems although it may alsobe employed for various other purposes.

Broadly, the invention consists'in including a photo electric cell incircuit with a thermionic valve system and arranging for the continuoussubjection of said system to electric current oscillations, persistenceof which is necessary to prevent any indication being given thatpret'letermined light conditions are departed from, the said currentoscillations being caused by the regular interruption of a beam of lightupon the cell aforesaid so that although the'latter may be exposed andnot screened, as is preferred, against all light except that of theregularly interrupted beam, the valve system will remain unaffected byvariations of steady illumination such as mark the change from day tonight.' The valve system may be such that it is at all times responsiveto persistence of oscillations as referred to or only at regularperiods,

Brealtdown or failure of such a system will at once afford an indicationjust as the presence of an obstruction in the path of the rays of theinterrupted beam is made known. In theaccompanymg drawings Figs. 1 and 2are diagrams illustrating two different ways of carrying out theinvention suitable for detectin' the presence of fog for example, Fig. 3bein a fragmentaryvicw of a. part of Fig. l tal ren at right angles.

As shown in Fig. 1, the light from a suitable source such as a lamp orprojector 1 intermittently reaches a collimating lens 2 throughapertures 3 of a pierced disc 4 continuously driven by a motor 5, therays from said-lens 2 being collected by another distant lens 6 anddirected on to a cell 7 which whilst it may be an ordinary selenium cellit is preferred should be one of a. very high resistance which may bealsospecially sensi tive to a particular part of the spectrum although acell sensitive to infra red i. e. heat rays and an ultra violetsensitive cell eras? may be employed, the said cell being intro-. I

duced into the grid circuit 8 of the first valve 9 of an audio frequencyvalve amplifier of one or more stages, the system shown being one thatis well known and per se forms no part of the present invention. Onevalve, in thiscase the final valve 10 is employed to rectify thealternating current delivered by the amplifier, and anode rectific'ationis availed of in preference to cumulative grid rectification.

The light rays from-the receiver lens 6 may be brought to a focus infront of the photo electric cell 7 at which point can be located adiaphragm or screen 11 to limit the amount of daylight that may haveaccess to the cell, and if desired a color filter or combination offilters may be employed in such diaphragm or screen which, as in thecase of cells scnsitive to special regions of the spectrum, enable aselective action to be obtained, as may be necessary or desirable indetecting haze and fog.

The indicating device may be any suitable form of relay associated withthe valve that efiects rectification, inthis case the valve 10, beingexemplified as a well known type of \Voston moving coil relay with thecoil 12 connected to lead 13 through lead 1 and through a lead 15 to apoint between battcry l6 and a smaller battery 17 connected in serieswith a regulating resistance 18. As long as the valve system remainsexcited by the reception of light impulses from the lamp 1 the battery16 will so preponderate over the battery 17 that the coil 12 will take aa position such that an arm 19 bears against a dead-contact 20. If,however, by reason of fog forexample the valve system is no longereffective the battery 17 will cause a reverse current to flow throughthe coil 12 and so move the arm 19 as to cause the contacts 21 in thelocal circuit of a hell or other suitable which normally results whenthe "oscillations of current derived with the aid of the photoelectriccell 7.

electric cell 7 become sutficiently feeble. By using adequateamplification the saturation current can be attained in the last valvel0 or equivalent so that unless light falls in intensity below apredetermined'value the relay will not act.

The lenses 2 and 6 referred to may be replaced by any other suitableoptical means.

The details may be varied in many ways, it being permissible for exampleto employ various other valve systems.-

As the continuous operation of the device in a satisfactory manner forvery long periods without alteration may be desirable,

clock work or similar mechanical means may be employed to disconnect thebatteries except for a very brief period, say every minute.

An arrangement of this kind is shown in Fig. 2 where three contact discs23, 24:, 25 are arranged to be collectively driven. The contact disc 23is of insulating material with a metallic strip 26 cooperating duringeach revolution with a pair of brushes 27 adapted to complete and openthe circuit of battery 28 associated with the photo- The contact disc24: is of metal but includes astrip 29 of insulating materialcooperating with a pair of brushes 30 associated with an auxiliary relaywinding 31 the armature 32 of which has a spring bias towards the deadcontact 33 when the relay is deenergized. The contact disc 25is ofinsulating material with a metallic strip 34 of two dill'erent widthswith which cooperate a pair of brushes 3.) adapted to complete .thecircuit between the large and small batteries 16 17 associated with themain relay embodying coil 12 as well as a brush 36 adapted to connectone end of the said coil to both batteries at the same point butonlyafter the connec 'tion between the batteries is established and todisconnect the said end of the coil before the connection between thebatteries is interrupted. One of the brushes 30 is connected by lead 37to one contact 38 of the main relay and the other brush 30 is connectedby lead 39 to a contact 40 adapted to be engaged by the armature 32 whenthe auxiliary relay is energized, said arma-- ture having a connection41 leading to a second contact. 42 of the main relay. The armature 32further carries an insulated contact 43 adapted to engage contacts 21 ofa local, circuit that includes the signal device or bell 22. Normallythe, parts oc cupy the the position shown from which it will be apparentthat the batteries 16, 17 and 28 are idle. During rotation of thedevices 23, 2t and 25 the circuit of bat tery 28 is completed throughbrushes 27 at the same time as brushes 35 act to connect the batteries16- and 17 together. Immediately afterwards brush36 acts to connect thecoil 12 of the main relay to such batteries. If there be no fog, thevalve system becomes active immediately the ci1- cuits or batteries 16,17 and 28 are complete and .the coil 12 of the main relay when connectedhas current established iii it instantly at its proper value. lhc resultis that the armature 1!) of the main relay. remains in the positionshown as in the.

first example described and no signal is given. If however by reason offog the valve system is not ell'ective battery 17,

disc and complete a holding circuit for sis:

battery 44: and relay coil 31 by way of the armature 32, contact it),lead 39 and part of lead 37, whereupon notwithstanding that the circuitsof batteries 16 17 and 28 are again interrupted at brushes 35 and 27 thesignal will continue to be given during the completion of the rotationof the discs. If during the next rotation of the discs the fog stillpersists the battery H: of the auxiliary relay will be again energizedfirst by the battery 17 as before, whilst the insulatlng strip 29 ofdisc 2% interrupts the holdin circuit, and subsequently by such holdingcircuit, but if there be no fog and the valve system is effective toprevent closure of the circuitof battery ll by the main relay, then thepassage of the insulating ip 29 of disc 24 under brushes 30 will resultin the auxiliary relay being released. The signal will thus no longeract.

In addition to the advantages already referred to the invention enablestransformers to be used for amplification whilst the employment of anintermittently interrupted beam of light overcomes the necessity ofhaving to resort to direct current amplification in which, as is known,it is dif ficult to obtain sulhciently steady conditions with batteriesand relays Other uses to which the invention may be put may be therecording or the passage of objects to be counted. For instance HQW'S.

papers or printed articles may be provided with dark zones adapted toenter-the path of continuously interrupted hght rays as referred to soas to constitute an obstruction 1. Light responsive means of the kindeferred to comprising a thermionic valve lar periods to the persistenceof the electric oscillations to which it is continuously subjected. c

2. Means of the hind herein referred to comprising a source of lightfrom which a bean; emanates, means for regularly interrupting such beam,a photo electric cell exposed to said interrupted beam of light, a

thermionic valve system with which the cell is operatively connected,indicating means rendered inoperative whilst the valve system IS subjectto the action of the regularly interrupted beam of light and'converselyrendered operative when the regularly interrupted beam of light isobscured, and means whereby the valve system is automatically renderedresponsive to the interrupted beam of light only at intervals.

3. In light responsive means of the kind herein referred to a thermionicvalve system embodying an audio frequency valve amplifier, an indicatingdevice, a-relay, a battery influencing said relay under control of thevalve system and a smallcr battery influencing the relay independentlyof the system, the said relay acting, when the larger battery isfunctioning, to revent the indicating device operatingan the smallerbattery at other times rendering the indicating device 0 erative,substantially as described.

'4. In ight responsive means of the hind herein referred to, a.thermionic valve sy8- tern embodying an audio frequency valve amplifier,an indicating device, a relay, a battery influencing said relay undercontrol of the valve system, a. smaller battery influencing the relayindependent of the system, a second relay influenced by the first namedrelay and means controlled by the first named relay for iniiuencin saidsecond relay when no longer influenced directly by the first relay, saidsecond relay being adapted to render the indicating device operative andinoperative, substantially as described.

5. In light responsive meansof the kind herein referred to, a thermionicvalve system, an indicating device, a relay directly associated with thesaid system, a relay directly associated with the first named relay andadapted to operate the indicating device and mechanically drivenswitching means adapted to render the valve system periodicallyinoperative, substantially as described.

6. In light responsive means of the kind referred to, a thermionic valvesystem, an indicating device, a relay directly associated with the saidsystem, a relay directly associated with the first shamed relay andadapted to operate the indicatin device, means for influencing the relayoil the indicating device independently of the first named relay,mechanically driven switching means adapted to render the valve systemperiodically inoperative and switch means also mechanically drivenadapted to control the relay of the indicating device, substantially asdescribed.

Signed at Dublin, of July, 1924:.

JOHN JGSEPH DOWLIHG.

lrela'nd, this 10th day

